Hydraulic braking systems have typically been the basis for vehicle braking systems, especially automotive braking systems. Hydraulic systems are used to convert fluid pressure into linear and/or mechanical motion. Such systems allow the source of the hydraulic pressure to be positioned remotely from the cylinders that effect the braking action. These systems comprise an actuator, such as a brake pedal, reservoir fluid responsive to pressure applied by the actuator, (such as a master cylinder) and means for converting the hydraulic pressure to a braking force, generally fluid cylinders. Mechanical braking pressure is achieved by utilizing the force of the depression of the brake pedal by the driver to increase the pressure on the master cylinder. Such systems are typically accompanied by a vacuum boost that multiplies the force supplied to the brake pedal, throughout the braking operation. The increased pressure in the master cylinder is then transmitted through fluid lines to the fluid cylinders. The fluid cylinders operate the calipers thereby forcing the calipers and brake pads against rotors or drums which slows the vehicle by frictional force.
Hydraulic systems of the above-described type have many disadvantages. These include the large amount of volume and mass that the master cylinder, vacuum booster, ABS modulator and hydraulic lines add to the completed vehicle. Installation of standard hydraulic braking systems is also complicated and labor intensive. Additionally, the large number of parts and installation also adds to repair and maintenance issues as individual parts reach the end of their useful life. A variant form of applying a vehicle brake system is referred to as a brake by wire brake system (BBW). BBW describes the ability to activate vehicle wheel brakes via an electric signal generated by an onboard processor/controller as a result of input signals thereto. Brake torque is applied to the wheels without direct mechanical interaction between the vehicle's brake pedal and the wheel brake.
A particular type of BBW systems is known as a "dry interface corner" system (DIC). The typical DIC system operates when a driver inputs a force to the brake pedal. A force sensor and travel sensor attached to the pedal transmits an electronic signal to an electronic controller, which in turn sends the signal to the self contained braking device typically located at each wheel of the vehicle. The DIC system is known as a hybrid system in that electric signals are used to generate the type and amount of braking force required at each wheel of the vehicle with electrical wires rather than standard hydraulic brake lines. Located at each corner of the vehicle is a self-contained module that takes the electrical signal and mechanically brakes the vehicle. The self-contained module utilizes an individual motor that drives a ball screw piston assembly that pressurizes hydraulic brake fluid to ultimately apply the brake caliper to a rotor at that corner of the vehicle. Such a DIC system significantly reduces assembly cost. The individual modules can be separately assembled and fluid filled prior to the manufacture of the vehicle. DIC modules then only need to be bolted to the automobile during the assembly process and plugged in using standard electrical connections. Thus, reliability and quality control of the overall brake system is also increased. Finally, the elimination of hydraulic lines stretching throughout the vehicle as well as the elimination of the master cylinder, booster, and ABS modulator reduces space requirements within the engine compartment.
Presently, fluid reservoirs are filled at the assembly plant through a reservoir cap using an evacuate-and-fill or bleeder ball technique. Because the cap is open, fluid may spill and create a mess. The final fill level may vary. Contamination may enter the fluid system through the open cap, blocking small passages and wearing finished surfaces.
Once the vehicle is on the road, field service may need to be performed on the braking module to assure reliable operation. Opening the reservoir cap can introduce contamination into the system, particularly since the DIC braking module is mounted near the ground where it can accumulate dirt and debris. Because of the location of the DIC braking module on the vehicle, it may be difficult to see the fluid level and to achieve the correct fluid level.
It would be desirable to have a dry interface corner assembly reservoir cap that would overcome the above disadvantages.